The present invention relates to brakes, particularly vehicular wheel brakes, that feature a rotary brake surface such as a wheel drum and a frictional braking member such as a shoe and lining assembly that is operative to be moved, preferably by an air actuated cam mechanism, against the rotary brake surface and frictionally retard and ultimately stop the rotary brake surface from rotating in a brake applied condition and to disengage and move away from the rotary brake surface in a brake disengaged condition such as when a vehicle operator steps upon and then releases a brake pedal.
Generally, there is an initially established desired clearance between the rotary brake surface and the frictional braking member when the braking system is new or newly repaired. However, due to wear of the frictional braking member over a period of time, the initial clearance is caused to increase resulting in a greater distance for the frictional braking member to travel before it engages the rotary brake surface. In other instances, heat may cause either or both the rotary brake surface and frictional braking member to swell and expand towards each other and thus reduce the clearance from the initially established clearance therebetween in the brake disengaged condition. Likewise, cold temperatures may cause either or both the rotary brake surface and frictional braking member to contract resulting in an increase in the clearance therebetween from the initially established clearance in the brake disengaged or released condition.
Thus, for a variety of reasons, the clearance between a rotary brake surface and a frictional braking member is undesirably apt to change from that originally established.
In view of the above, a need exists to simply and economically sense changes in the brake clearance from the initial clearance desired and preferably automatically adjust the clearance sensed to the initial clearance desired.
The present invention solves the problem in a novel way by utilizing pressurized air to sense the brake clearance in a simple and effective manner and provide a signal indicative thereof which preferably is utilized by a brake clearance adjusting device to automatically adjust the brake clearance to the initial clearance desired in the brake disengaged condition which is particularly advantageous for vehicles driven by engines and equipped with an on-board source of pressurized air driven by the engine.